The Foreign Office has admitted failing to make complaints on behalf of British nationals who say they have been tortured after being detained overseas during counter-terrorism investigations.

Officials say they made no complaint to the Pakistani government on behalf of one man who was detained there and allegedly tortured. They also appear to have made no effort to pursue complaints made on behalf of three other British men after they were allegedly tortured in Pakistan.

The FCO has also disclosed that two other men, who were held in either Bangladesh or Syria during counter-terrorism investigations, have alleged that they were tortured, but admits that it has not made any complaint on their behalf - and is refusing to identify in which of the two countries they were held.

Officials have also admitted that they have made no complaint on behalf of Azhar Khan, 26, from Slough, whose allegations of appalling mistreatment in Egypt were reported by the Guardian yesterday. The Foreign Office is refusing to give full details of how it dealt with his case, saying it is concerned about his rights under the Data Protection Act. "The FCO takes data protection seriously, and we would not want to place Mr Khan in a position where he felt that his rights under the act had potentially been compromised," a spokesman said.

Khan's allegations raise new concerns about official British complicity in torture. He is an associate of a group of al-Qaida-inspired terrorists who plotted a huge bomb attack in the south-east of England in 2004, and is the former brother-in-law of the leader of the group. He was arrested at the same time as the group in March 2004 but released without charge.

He was detained after flying to Cairo in July last year, and says he spent five days being questioned under torture about the group and about other friends in Slough, Crawley in West Sussex, and east London, whose names have not entered the public domain. He says the Egyptian intelligence officers also questioned him, under torture, about discrepancies between a statement he gave to the Metropolitan police when he was arrested in 2004 and comments he subsequently made while visiting friends in prison in the UK.

He says he was forced to stand on the same spot for five days, naked but for a hood over his head, handcuffed and with his feet shackled. He says that he received regular beatings, was occasionally subjected to electric shocks, and that others were being tortured in the same large room.

The Foreign Office's admission came in answers to parliamentary questions tabled by Andrew Tyrie, the Conservative MP who chairs the all-party parliamentary group on extraordinary rendition. Lawyers representing British nationals who have been tortured in Pakistan believe that the reason for the FCO's lack of enthusiasm to make and pursue complaints of ill-treatment is that these individuals were detained at the request of British authorities, including MI5, and that British intelligence officers were aware that they were being tortured.

After yesterday's report on the allegations made by Khan, Clara Gutteridge, of Reprieve, the legal charity that represents Binyam Mohamed, said: "After similar cases in Pakistan and Guantánamo Bay, Azhar Khan's story indicates that the virus of British involvement in torture also spread to Egypt. Sad to say we have further evidence of UK involvement with abusive regimes around the world, including Kenya, Ethiopia, Afghanistan and Iraq. Enough is enough. The British government must come clean and reveal exactly what happened to the victims, where they are now, and what is being done to make things right."